This invention is directed to an event sensor, as for instance a pH sensor and a process for the preparation of such a sensor. The sensor utilizes a dye which is sensitive to an event. The dye is attached to a finely divided polymeric material as for instance cellulose. The polymeric material, bearing the dye thereon, is dissolved in a solvent and is deposited on an optical surface of an optical fiber. The polymeric material, bearing the dye, is regenerated from the solution to form a solid matrix of the polymeric material, bearing the dye, on the optical surface of the optical fiber.
The determination of an event, as for instance the hydrogen ion concentration or pH of a solution, is very important in many situations. One of theses is the determination of the pH of biological specimens, as for instance, blood. The pH of the blood is indicative of many physiologically important conditions of a patient.
In constructing event sensors it is necessary to construct them of a material which is permeable to an indicator of the event being measured. For a pH sensor, the material must be permeable to ionic species. This severely limits the types of material which may be used for such sensors.
Glass pH electrodes have been used for years for pH determinations. These glass electrodes have to be dipped into a solution for determination of the pH of the solution. In a medical situation, such as a patient recovering from a myocardial infarction, it would be advantageous to be able to measure the pH event in real time, that is continuously. Unfortunately this is not possible with glass electrodes. With glass electrodes, at best, only intermittent measurements can be made. Each of the seperate measurements requires withdrawal of an aliquot of blood from the patient and sending the blood sample to the laboratory for the determination of the pH of the patient's blood. Aside from the requirement of having to continuously withdraw the aliquots of blood, this procedure is time consuming and as such it does not give a true reflection of the patient's condition in real time.
For biological fluids, a prior known sensor uses the fluorescent properties of a dye in conjunction with the ionic permeability of a preformed integral cellulose membrane sheet. In this sensor, the cellulose membrane is chemically treated so as to introduce covalent bondable groups onto the membrane. The dye is then covalently bonded to these groups to adhere the dye to the membrane. A small disk is cut from the membrane sheet and is attached to a cassette in association with an optical fiber bundle also attached to the cassette. When the dye is excited by excitation light imposed on the dye along the fibers, it under goes fluorescence, emitting a wavelength of light at a different wavelength than the excitation wavelength. The emission light is measured as an indication of the pH.
In constructing the above sensor, it is important to insure that the dye is evenly distributed across the membrane sheet such that there will be reproducibility between individual disks cut from the membrane sheet. Aside from evenly disbursing the dye molecules across the membrane, it is also important to insure that the dye molecules are placed with respect to one another such that there is a sufficient concentration to be responsive to pH changes in the solution being measured. Because of these considerations, it is necessary to perform quality control procedures on each disk cut from the membrane to insure that the distribution of the dye on the cellulose membrane is sufficient to render the individual disk useful as a pH sensor.
The above noted cellulose membranes utilize a commercial cellulose membrane as for instance a cellulose membrane suitable for use as a dialysis membrane. The intact membrane is first treated with cyanogen bromide followed by a condensation with an appropriate amine, for instance hexamethylenediamine. This yields a compound which has a primary amino functional group which is reacted with the dye, to attach the dye to the membrane. This method does not lend itself easily to the fabrication of a microsensor on an optical fiber tip which is on the order of 0.006 inches in diameter.